Many attempts have been made to measure position using linear and rotary position measurement devices that employ a wide variety of different types of position sensing systems using different types of position sensing head arrangements, sensing elements, circuits, techniques and methods with varying degrees of success. Many of these position measurement devices have position determining systems equipped with a fine position sensing system used to determine fine position and a coarse position sensing system designed to determine and retain a position state using power generated by the coarse position sensing system during coarse position sensing system operation. Such position measurement devices equipped with coarse position sensing systems configured to at least partially or even completely power the position determining system are expensive, are relatively inflexible in their implementation, and can suffer coarse position determination problems.
One example of such position measurement device is the angle of rotation position sensing device disclosed in U.S. Pat. No. 6,084,400 equipped with a self-powered position determining system having a fine position sensing system and coarse position sensing system self-powered by the coarse position sensing system without the use of any battery or external power supply. The fine position sensing system is provided by a fine angle rotation sensor, such as in the form of a magnetic or optical encoder or resolver, linked to the rotary shaft and is used to relatively precisely sense an angle of the shaft. The coarse position sensing system is provided by a shaft rotation counter formed of an arrangement of radially extending Wiegand wires circumferentially spaced apart about part of the shaft with electrical pulses from the Wiegand wires during shaft rotation that provide shaft rotation count while also powering the position determining system.
Another example is the absolute position measurement device disclosed in U.S. Pat. No. 8,283,914, which discloses a position determining system having a fine position sensing system using hall sensors and a coarse position sensing system using Wiegand wires and another hall sensor. Electrical pulses from the Wiegand wires generated during shaft rotation can be used to power an electronic management unit that updates a counting unit having non-volatile memory storage with coarse position data while also storing some of the electrical pulse energy for later use. External power can be supplied to a fine resolution counting or position measurement logic unit that processes the fine position sensor data from the fine position sensing hall sensors and the coarse position data to provide position information via a user interface to a user or operator.
These types of position determining systems are generally limited to use in rotary position sensing devices, including shaft turn counters and multiple-turn absolute position sensing devices. Even where adapted for use in linear position measurement applications, the components required to eliminate or minimize the need for a battery or use of an external supply include types of non-volatile memory, such as ferromagnetic RAM, and other low power components, such as very low power gate arrays, which are expensive, add complexity, inflexible and can limit the resolution of fine position determination that can be achieved.
What is needed is an improved position measurement device that can be equipped with a battery, yet which minimizes power usage, all without requiring such expensive low power components found in the prior art.